The present invention relates to a battery controller for controlling batteries of different kinds and more particularly to a battery controller for controlling batteries of different kinds which are equipped in a portable information processing apparatus or communication apparatus. Further, the present invention relates to a note-type personal computer equipped with the battery controller.
Conventional apparatuses such as note-type personal computers, portable telephones, portable cassette players and handy video cameras include a battery for supplying electric power to internal circuits provided in the apparatuses when an external power supply is not connected thereto.
A battery used in the portable information processing apparatus or the like includes a NiCd battery, a NiMH battery or a Li ion battery.
The NiCd battery uses nickel for a positive pole and cadmium for a negative pole and has excellent low temperature characteristic and overcharge/overdischarge resistant characteristic. Further, the NiCd battery has a long life and a low manufacturing cost but has problems such as a large memory effect, a low electric power capacity per unit weight and environmental disruption due to cadmium.
The memory effect is one of characteristic of a secondary battery which can be re-charged. When the battery is re-charged in the state where electric power in the battery is not discharged completely, the battery memorizes the charge level remaining therein upon the re-charging operation and when the charge level remaining upon the re-charging operation is reached in the re-discharging operation, the battery stops the discharging although electric power in the battery is not discharged completely.
The NiMH battery uses nickel for a positive pole and hydrogen-occluding alloy for a negative pole and has a larger electric power capacity per unit weight and a smaller memory effect as compared with the NiCd battery.
The Li battery uses material which occludes and emits lithium ions in positive and negative poles and generally uses LiCoO.sub.2 for the positive pole and carbon for the negative pole.
The Li ion battery has an excellent feature that the electric power capacity per unit weight is larger than the NiMH battery and there is no memory effect, while since the Li ion battery has cobalt contained in the positive pole thereof, it is difficult to reduce a manufacturing cost of the positive pole and a peripheral circuit for preventing reduction of the safety and deterioration of the performance upon the overcharging operation is indispensable for the Li ion battery.
Further, various batteries used in the conventional portable information processing apparatus or the like have different charging and discharging characteristics.
More particularly, a constant-current charging system is used to charge the NiMH battery. The NiMH battery is charged by a rapid charging current recommended by a battery maker and a temperature of the battery is detected at a thermistor terminal thereof to finish the charging.
In addition, a constant-current and constant-voltage charging system is used to charge the Li ion battery. In the constant-current and constant-voltage charging system, the battery is first charged by a constant current and when a terminal voltage of the battery reaches a predetermined value, the battery is switched to be charged by a constant voltage and then after an elapse of predetermined time the charging is finished.
As different points of the discharging characteristics of the NiMH battery and the Li ion battery, a very low battery voltage and a final or termination voltage are different.
The very low battery voltage is a voltage at which an apparatus equipped with the battery is shifted to a suspended mode. In portable personal computers or the like, the operation mode is shifted to the suspended mode when this voltage is reached, to prevent stoppage of supply of electric power.
Further, the termination voltage is a voltage for stopping supply of electric power by the battery. Since there are any cells in which discharging is insufficient when the termination voltage is too high and which is overdischarged when the termination voltage is too low, it is necessary to set the termination voltage carefully.
In the conventional portable information apparatus or the like, the charging and discharging characteristics are largely different depending on a kind of a battery mounted therein and accordingly the apparatus cannot use a battery of different kind.